Grease composition for ball type constant velocity joints and ball type constant velocity joints containing the grease composition

ABSTRACT

A grease composition for use in ball type constant velocity joints, which comprises the following components a base oil; a diurea thickener of the formula: 
 
R 1 —NH—CO—NH—C 6 H 4 -p-CH 2 —C 6 H 4 -p-NH—CO—NHR 2  
 
wherein R 1  and R 2  are alkyl groups having 8 carbon atoms, molybdenum disulfide; molybdenum dithiocarbamate of the formula: 
 
(R 3 R 4 N—CS—S) 2 —Mo 2 OmSn 
 
wherein R 3  and R 4  independently represent an alkyl group having 1 to 24 carbon atoms, m is 0 to 3, n is 4 to 1 and m+n=4, calcium salts or overbasic calcium salts of petroleum sulfonates, sulfur-phosphorus extreme pressure agent, and castor oil. The grease composition exhibits excellent wear-resistance and pitting-inhibitory effect.

BACKGROUND OF THE INVENTION

The present invention relates to a grease composition for use in highcontact pressure ball type constant velocity joints, in particular,plunging or fixed ball type constant velocity joints. A very highcontact pressure is developed between parts of constant velocity jointsto be lubricated and the joint parts undergo complicated rolling andsliding motions. This often results in abnormal wear and metal fatigueand, in turn, leads to a spalling phenomenon, i.e., pitting of the jointparts. More specifically, the present invention relates to a greasecomposition for ball type constant velocity joints which can effectivelylubricate such constant velocity joints to effectively reduce wear ofjoints and to effectively reduce occurrence of pitting in the parts tobe lubricated.

Examples of lubricating greases conventionally used in such constantvelocity joints include a lithium soap thickened extreme pressure greasecontaining molybdenum disulfide and a lithium soap thickened extremepressure grease containing molybdenum disulfide and sulfur-phosphorusextreme pressure agents or a lead naphthenate. However, these greasesfor constant velocity joints have not always been satisfactory in thesevere working conditions which occur in the recent high-performancemotorcars.

Recently, the number of four-wheel drive (front engine, front drivetype) motorcars have rapidly increased. Motorcars are being made lighterto improve fuel consumption. It is therefore necessary to make constantvelocity joints used in these motorcars as lighter and smaller aspossible.

The double offset type constant velocity joints and cross groove typeconstant velocity joints used as plunging type constant velocity jointsas well as Birfield joints used as fixed type constant velocity jointshave a structure in which torques are transmitted through 6 balls.

These joints cause complicated reciprocating motions such as complicatedrolling and sliding motions during rotation at a high contact pressure.Therefore, stresses are repeatedly applied to the balls and the metalsurfaces which come in contact with the balls and accordingly, thepitting phenomenon is apt to occur at such portions due to metalfatigue.

The recent improvement in the power of engines is accompanied by anincrease in the contact pressure as compared with conventional engines.Motorcars are being made lighter to improve fuel consumption and thesize of joints has correspondingly been down-sized. This leads to arelative increase in the contact pressure and thus the conventionalgreases are not sufficient to reduce the pitting phenomenon. Inaddition, the greases must also be improved in their heat resistance.

For this purpose, there are proposed a grease composition for use inconstant velocity joints, which comprises a urea thickener, molybdenumdisulfide and at least one member selected from the group consisting ofcalcium salts of oxidized waxes, calcium salts of petroleum sulfonates,calcium salts of alkyl aryl sulfonates, calcium salts of salicylate,calcium salts of phenates, overbasic calcium salts of oxidized waxes,overbasic calcium salts of petroleum sulfonates, overbasic calcium saltsof alkyl aryl sulfonates, overbasic calcium salts of salicylate, andoverbasic calcium salts of phenates (JP-A-9-194871 (=U.S. Pat. No.5607906, EP 773280 B1)) and a grease composition for use in constantvelocity joints, which comprises, in addition to the above components, ametal-free sulfur-phosphorus extreme pressure agent and molybdenumdithiocarbamate (JP-A-9-324189 (=EP 811675 B1)).

However, these greases for constant velocity joints have not always showsatisfactory pitting-inhibitory effect when they are used in highcontact pressure ball type constant velocity joints.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a greasecomposition for use in high contact pressure ball type constant velocityjoints which has an excellent pitting-inhibitory effect as compared withconventional grease compositions for constant velocity joints, and balltype constant velocity joints containing the grease composition.

The inventors of this invention have conducted various studies todevelop a grease composition having improved durability and found thatthe addition of vegetable fats and oils to a conventional constantvelocity joint improves the durability of the joints and optionally theincrease of relative amount of sulfur-phosphorus extreme pressure agentfurther improves the durability of the joints. The present invention hasbeen accomplished based on this finding. The present invention providesa grease composition for use in ball type constant velocity joints andball type constant velocity joints containing the grease composition asshown below.

1. A grease composition for use in ball type constant velocity joints,which comprises the following components:

(a) a base oil selected from the group consisting of mineral oils, ethertype synthetic oils, ester type synthetic oils, hydrocarbon typesynthetic oils and mixture thereof,

(b) a diurea thickener represented by the following formula:R¹—NH—CO—NH—C₆H₄-p-CH₂—C₆H₄-p-NH—CO—NHR²

wherein R¹ and R² are alkyl groups having 8 carbon atoms,

(c) molybdenum disulfide;

(d) a molybdenum dithiocarbamate represented by the following formula:(R³R⁴N—CS—S)₂—Mo₂OmSn

wherein R³ and R⁴ independently represent alkyl groups having 1 to 24carbon atoms, m is 0 to 3, n is 4 to 1 and m+n=4,

(e) at least one calcium salt selected from the group consisting ofcalcium salts of petroleum sulfonates, and overbasic calcium salts ofpetroleum sulfonates,

(f) a sulfur-phosphorus extreme pressure agent in an amount of 1.5 to10% by weight on the basis of the total weight of the composition, and

(g) vegetable fats and oils.

2. The grease composition of claim 1, wherein the grease composition isfor use in high contact pressure ball type constant velocity joints.

3. The grease composition of claim 1 or 2, wherein the greasecomposition comprises, on the basis of the total weight of thecomposition, 1 to 25% by weight of the diurea thickener; 0.1 to 5.0% byweight of the molybdenum disulfide; 0.1 to 5.0% by weight of themolybdenum dithiocarbamate; 0.1 to 5.0% by weight of the calcium salt;1.5 to 10% by weight of the sulfur-phosphorus extreme pressure agent,and 0.1 to 3.0% by weight of the vegetable fats and oils.

4. The grease composition of any one of claims 1 to 3, wherein thegrease composition comprises, 2.0 to 5.0% by weight of thesulfur-phosphorus extreme pressure agent.

5. The grease composition of any one of claims 1 to 4, wherein thegrease composition is for use in the ball type fixed constant velocityjoints.

6 A ball type constant velocity joint, wherein the grease composition ofany one of claims 1 to 4 is contained.

The grease composition of the present invention for use in ball typeconstant velocity joints greatly improves pitting-inhibitory effect andremarkably extends the life of the constant velocity joints containingthe grease composition. These effects of the present invention areoutstanding when the grease composition is used in constant velocityjoints which are used under high contact pressure condition.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the grease composition for use in ball type constantvelocity joints of the present invention will be described in detail.

The grease compoisition of the present invention comprises the followingcomponents (a), (b), (c), (d), (e), (f) and (g).

(a) a base oil selected from the group consisting of mineral oils, ethertype synthetic oils, ester type synthetic oils, hydrocarbon typesynthetic oils and mixture thereof,

(b) a diurea thickener represented by the following formula:R¹—NH—CO—NH—C₆H₄-p-CH₂—C₆H₄-p-NH—CO—NHR²

wherein R¹ and R² are alkyl groups having 8 carbon atoms,

(c) molybdenum disulfide;

(d) a molybdenum dithiocarbamate represented by the following formula:(R³R⁴N—CS—S)₂—Mo₂OmSn

wherein R³ and R⁴ independently represent alkyl groups having 1 to 24carbon atoms, m is 0 to 3, n is 4 to 1 and m+n=4,

(e) at least one calcium salt selected from the group consisting ofcalcium salts of petroleum sulfonates, and overbasic calcium salts ofpetroleum sulfonates,

(f) a sulfur-phosphorus extreme pressure agent in an amount of 1.5 to10% by weight on the basis of the total weight of the composition, and

(g) vegetable fats and oils.

First, Component (a) will be explained.

The base oil as Component (a) is not restricted to specific ones and maybe, for instance, lubricating oils currently used such as mineral oils,ether type synthetic oils, ester type synthetic oils, hydrocarbon typesynthetic oils or mixture thereof. From the economical point of view,mineral oils are preferred, and a mixture of mineral oils as a majorcomponent and synthetic oils is also preferred.

Kinetic viscosity of the base oils at 100° C. is preferably 5 to 30mm²/s, more preferably 7 to 25 mm²/s. If the viscosity is less than 5mm²/s, high-speed durability of constant velocity joints isinsufficient, while if it is greater than 30 mm²/s, high-speeddurability of constant velocity joints decreases.

The diurea thickener as Component (b) can be obtained by a reactionbetween diphenylmethane diisocyanate and octylamine. The reaction is notlimited to specific ones but can be done by any known ones.

The molybdenum disulfide as Component (c) has widely been used as anextreme pressure agent. With regard to the lubricating mechanismthereof, the molybdenum disulfide is easily sheared under the slidingmotions through the formation of a thin layer since it has a layerlattice structure and it shows effects of reducing friction and ofpreventing seizure of joints. There have been known molybdenum disulfideproducts having various particle sizes, but it is preferable, in thepresent invention, to use those having a particle size ranging from 0.25to 10 μm, in particular, 0.55 to 0.85 μm expressed in terms of anaverage particle size as determined by the method called Fisher method(by the use of a Fisher Sub-Sieve sizer).

The calcium salts or overbasic calcium salts as Component (e) areselected from those known as metal cleaning dispersants orrust-inhibitors which are used in lubricants such as engine oils, suchas calcium salts of petroleum sulfonates and overbasic calcium salts ofpetroleum sulfonates which are obtained by sulfonation of aromatichydrocarbon in lubricating oil fraction.

Preferred sulfur-phosphorus extreme pressure agents as Component (f)have a sulfur content ranging from 15 to 35% by weight and a phosphoruscontent ranging from 0.5 to 3% by weight and exhibits excellent effectsof inhibiting wear and of preventing seizure of the joints through thewell-established balance between the sulfur and phosphorus contents.More specifically, if the sulfur content exceeds the upper limit definedabove, joints are easily corroded, while if the phosphorus contentexceeds the upper limit defined above, wear-inhibiting effect cannot beexpected. On the other hand, if sulfur or phosphorus content is lessthan the corresponding lower limit, desired wear-inhibiting andseizure-preventing effect cannot be expected.

Examples of the vegetable oils and fats as Component (g) include castoroil, rapeseed oil and linseed oil. Among them, castor oil isparticularly preferred.

Preferably, the grease composition for use in ball type constantvelocity joints of the present invention comprises, on the basis of thetotal weight of the composition, 1.0 to 25.0% by weight of the diureathickener (b), 0.1 to 5.0% by weight of molybdenum disulfide (c), 0.1 to5.0% by weight of the molybdenum dithiocarbamate (d), 0.1 to 5.0% byweight of the calcium salt (e), 0.1 to 5.0% by weight of thesulfur-phosphorus extreme pressure agent (f) and 0.1 to 3.0% by weightof the vegetable fats and oils (g).

If the amount of the diurea thickener (b) is less than 1% by weight, thethickening effect thereof tends to become too low to convert thecomposition into a grease, while if it exceeds 25% by weight, theresulting composition tends to become too hard to ensure the desiredeffects of the present invention.

If the amount of the molybdenum disulfide (c) is less than 0.1% byweight, it becomes difficult to obtain the desired effects of thepresent invention, while if it exceeds 5% by weight, the effects of thepresent invention may be saturated.

If the amount of the molybdenum dithiocarbamate (d) is less than 0.1% byweight, it becomes difficult to obtain the desired effects of thepresent invention, while if it exceeds 5% by weight, the effects of thepresent invention may be saturated.

If the amount of the calcium salt (e) is less than 0.1% by weight, itbecomes difficult to obtain the desired effects of the presentinvention, while if it exceeds 5% by weight, the effects of the presentinvention may be saturated.

If the amount of the sulfur-phosphorus extreme pressure agent (f) isless than 0.1% by weight, it becomes difficult to obtain the desiredeffects of the present invention, while if it exceeds 5% by weight, theeffects of the present invention may be saturated.

If the amount of the vegetable fats and oils (g) is less than 0.1% byweight, it becomes difficult to obtain the desired effects of thepresent invention, while if it exceeds 3% by weight, the effects of thepresent invention may be saturated.

The grease composition for use in ball type constant velocity joints ofthe present invention may further comprise, in addition to the abovecomponents (a) to (g), antioxidants, rust inhibitors, and polymeradditives which are generally used in conventional lubricating oils andgreases. Moreover, extreme pressure agents, friction alleviating agents,agents for wear-resistance, and solid lubricating agents other than theabove components (c), (d), (e) and (f) may be added to the greasecomposition of the present invention. If these additives are used, theamount thereof is preferably 0.1 to 10% by weight of the total weight ofthe grease composition.

The present invention will hereunder be described in more detail withreference to the following non-limitative working Example andComparative Examples.

EXAMPLE 1

There were added, to a container, 440 g of a base oil and 58.9 g ofdiphenylmethane-4,4′-diisocyanate and the mixture was heated to atemperature between 70 and 80° C. To another container, there were added440 g of a base oil, 61.1 g of octylamine followed by heating at atemperature between 70 and 80° C. and addition thereof to the foregoingcontainer. The mixture was then reacted for 30 minutes with sufficientstirring, the temperature of the reaction system was raised up to 160°C. with stirring and the reaction system was allowed to cool to give abase aliphatic amine diurea grease. To the base grease, there were addedthe following additives listed in Table 1 in amounts likewise listed inTable 1 and an optional and additional amount of the base oil and thepenetration of the resulting mixture was adjusted to No. 1 grade by athree-stage roll mill.

A mineral oil having the following properties was used as the base oilfor the grease. Viscosity: at 40° C. 230 mm²/s at 100° C. 20 mm²/sViscosity Index: 100

COMPARATIVE EXAMPLES 1 TO 3

The same procedures as in Example 1 were repeated to prepare a grease ofComparative Example 1 except that castor oil was not added, or a greaseof Comparative Example 2 except that the amount of sulfur-phosphorusextreme pressure agent was changed to 1% by weight.

A commercially available grease composition for use in constant velocityjoints containing graphite, organic molydenum and sulfur-phosphorusextreme pressure agent in molybdenum disulfide was used as a grease ofComparative Example 3.

The details of the components in Table 1 are as follows and unit of thenumerical values in the table is % by weight.

-   Molybdenum dithiocarbamate A (Trade name; Molyvan A available    from R. T. Vanderbilt)-   Calcium salt of petroleum sulfonate (Trade name; Sulfol Ca-45    available from Matsumura Petroleum Laboratory Co., Ltd.)-   Sulfur-phosphorus extreme pressure agent (Trade name; Anglamol 99    available from Lubrizol Japan)-   Castor oil (available from Hokoku Corporation)

Physical properties of these grease compositions were evaluatedaccording to the methods detailed below. Penetration thereof are alsosummarized in Table 1.

[Penetration] According to JIS K 2220 5.3

[Joint Durability Test]

Joint Type: Fixed type ball joint

Joint Size: BJ87

Angle of Joint: 6°

Number of Revolution: 200 rpm

Torque:

-   -   Joint durability test 1        -   900 Nm (conventional conditions under high torque load)    -   Joint durability test 2

1000 Nm (special conditions under torque load limit) TABLE 1 Comp. Comp.Comp. Components Example 1 Example 1 Example 2 Example 3 Aliphaticdiurea 91 92 93 base grease Molybdenum disulfide 2 2 2 Molybdenum 1 1 1dithiocarbamate A Ca salt of petroleum 2 2 2 sulfonate Sulfur-phosphorusex- 3 3 1 treme pressure agent Castor oil 1 — 1 Penetration 325 330 332330 Joint durability test 12,000,000 9,000,000 8,000,000 8,000,000 1(total number of revolution) Joint durability test 8,500,000 5,300,0005,000,000 4,500,000 2 (total number of revolution)

The results demonstrate that the grease composition for constantvelocity joint of Example 1 of the present invention containing castoroil and 3% by weight of the sulfur-phosphorus extreme pressure agentshows better pitting-inhibitory effect, in particular at high contactpressure than those of Comparative Examples 1 and 3 which do not containcastor oil or Comparative Example 2 wherein the amount of thesulfur-phosphorus extreme pressure agent is 1% by weight.

1. A grease composition for use in ball type constant velocity joints,which comprises the following components: (a) a base oil selected fromthe group consisting of mineral oils, ether type synthetic oils, estertype synthetic oils, hydrocarbon type synthetic oils and mixturethereof, (b) a diurea thickener represented by the following formula:R¹-NH-CO-NH-C₆ H₄-p-CH₂-C₆ H₄-p-NH-CO-NHR2 wherein R¹ and R² are alkylgroups having 8 carbon atoms, (c) molybdenum disulfide; (d) a molybdenumdithiocarbamate represented by the following formula:(R³R⁴N-CS-S)₂-Mo₂OmSn wherein R³ and R⁴ independently represent alkylgroups having 1 to 24 carbon atoms, m is 0 to 3, n is 4 to 1 and m+n=4,(e) at least one calcium salt selected from the group consisting ofcalcium salts of petroleum sulfonates, and overbasic calcium salts ofpetroleum sulfonates, (f) a sulfur-phosphorus extreme pressure agent inan amount of 1.5 to 10% by weight on the basis of the total weight ofthe composition, and (g) vegetable fats and oils.
 2. The greasecomposition of claim 1, wherein the grease composition is for use inhigh contact pressure ball type constant velocity joints.
 3. The greasecomposition of claim 1, wherein the grease composition comprises, on thebasis of the total weight of the composition, 1 to 25% by weight of thediurea thickener; 0.1 to 5.0% by weight of the molybdenum disulfide; 0.1to 5.0% by weight of the molybdenum dithiocarbamate; 0.1 to 5.0% byweight of the calciumd salt; 1.5 to 10% by weight of thesulfur-phosphorus extreme pressure agent, and 0.1 to 3.0% by weight ofthe vegetable fats and oils.
 4. The grease composition of claim 1,wherein the grease composition comprises, 2.0 to 5.0% by weight of thesulfur-phosphorus extreme pressure agent.
 5. The grease composition ofclaim 1, wherein the grease composition is for use in the ball typefixed constant velocity joints.
 6. A ball type constant velocity joint,wherein the grease composition of claim 1 is contained.
 7. A ball typeconstant velocity joint, wherein the grease composition of claim 3 iscontained.
 8. A ball type constant velocity joint, wherein the greasecomposition of claim 4 is contained.